
word = "bottles"                                      将值“bottles”（一个字符串）赋给一个名为“word”的新变量
for beer_num in range (99,0,-1):                      循环次数为从99依次减1倒数到0以beer_num为迭代变量
    print(beer_num, word, "of beer on the wall.")     这4个print函数调用显示当前迭代的歌词“99 bottles of beer on the wall.99 bottle of beer.Take one down.Pass it around.” ,  
    print(beer_num, word, "fo beer.")                 每次迭代时以此类推
    print("Take one down.")
    print("Pass it around.")
    if beer_num == 1:                                 查看次数是否是最后一轮，如果是，则结束歌词
        print("No more bottles of beer on the wall.")
    else:                                             否则...
        new_num = beer_num - 1                        把下一瓶啤酒记在另一个编号为“new_num”之中
        if new_num ==1:                               如果我们要进行到最后一瓶啤酒
            word = "bottle"                           要修改“word”变量的值
        print(new_num, word, "of beer on the wall.")  补充这次迭代的歌词
    print()                                           在迭代的最后打上空行，完成所有的迭代，程序结束
 
